This invention is a modification of U.S. patent application entitled xe2x80x9cImproved Safety Syringexe2x80x9d (hereinafter called as xe2x80x9cprior applicationxe2x80x9d) filed on: Sep. 6, 2001 by the same inventor of this application.
The prior application disclosed a safety syringe having a shank portion of the needle device locked on the syringe cylinder without being rotatable for enhancing a smooth coupling of the needle on the shank portion when assembling the needle device on the syringe cylinder.
However, the prior application is designed for hypodermic injection purpose, not suitable for intravenous injection.
The present inventor has found the drawbacks of the prior application and invented the present safety syringe for intravenous injection.
The object of the present invention is to provide a safety syringe for intravenous injection including: a syringe cylinder having a plurality of sleeve ribs formed in a sleeve portion eccentrically formed on the syringe cylinder, a needle device having a needle detachably coupled on an shank portion which is provided with a plurality of shank ribs on the shank portion to be engaged with the sleeve ribs in the sleeve portion, with the needle device retractable in and automatically biased in the syringe cylinder to prevent outward protruding of used needle; whereby upon external connecting and rotative coupling of the needle on the shank portion, the shank portion will be locked without being rotatable, thereby enhancing a smooth coupling of the needle on the shank portion of the needle device.
Another object of the present invention is to provide a safety syringe for intravenous injection including an annular extension annularly formed on an inside wall of the syringe cylinder adjacent to a rear end of the syringe cylinder and at least a ratchet tooth formed on a front portion of a plunger slidably held in the syringe cylinder; whereby the annular extension provides a stopper for preventing a rearward releasing of the plunger from the cylinder since the ratchet tooth on the plunger will be. locked against the annular extension when accidentally pulling the plunger rearwardly outwardly.
Still another object of the present invention is to provide a safety syringe for intravenous injection having at least a pair of beads or protrusions formed on an inside wall of the syringe cylinder to longitudinally guide the plunger rod, without being rotatable, for ensuring the coupling of the plunger socket with the needle locking head when coupling the plunger with the needle device.